Persist sidebar visibility across app launches

Closes #372

Tusker/Screens/Main/MainSplitViewController.swift

@@ -24,6 +24,15 @@ class MainSplitViewController: UISplitViewController {
         viewController(for: .secondary) as? SplitNavigationController
     }
     
+    private var sidebarVisibile: Bool {
+        get {
+            (UserDefaults.standard.object(forKey: "MainSplitViewControllerSidebarVisible") as? Bool) ?? true
+        }
+        set {
+            UserDefaults.standard.set(newValue, forKey: "MainSplitViewControllerSidebarVisible")
+        }
+    }
+    
     init(mastodonController: MastodonController) {
         self.mastodonController = mastodonController
         
@@ -45,6 +54,11 @@ class MainSplitViewController: UISplitViewController {
         sidebar.sidebarDelegate = self
         setViewController(sidebar, for: .primary)
         primaryBackgroundStyle = .sidebar
+        if sidebarVisibile {
+            show(.primary)
+        } else {
+            hide(.primary)
+        }
 
         let splitNav = SplitNavigationController()
         setViewController(splitNav, for: .secondary)
@@ -355,6 +369,18 @@ extension MainSplitViewController: UISplitViewControllerDelegate {
             return
         }
     }
+    
+    func splitViewController(_ svc: UISplitViewController, willHide column: UISplitViewController.Column) {
+        if column == .primary {
+            sidebarVisibile = false
+        }
+    }
+    
+    func splitViewController(_ svc: UISplitViewController, willShow column: UISplitViewController.Column) {
+        if column == .primary {
+            sidebarVisibile = true
+        }
+    }
 }
 
 extension MainSplitViewController: MainSidebarViewControllerDelegate {